There are many applications for sensors such as photoelectric sensors. These devices are used in many industrial applications to detect, for example, the presence or absence of a part on an assembly line. Such devices might, for example, incorporate a photoelectric transmitter and receiver which detects the presence or absence of varying amounts of light transmitted from the transmitter and received by the receiver as an indication of the presence or absence or type of the part on the assembly line. In other examples, an inductive sensor might incorporate an excitation oscillator (transmitter) and a receiver which detects the presence or absence or change in frequency of varying amounts of magnetic field originated by the transmitter.
In the industrial environment, there are many applications for such devices. Each application, in general, must be individually engineered and adjusted so that it functions properly within the parameters of the installation. For example, for a given transmitter output level, a small amount of receiver gain is needed in order to detect an object which is only a short distance away from the sensor. However, much larger receiver gain is required to detect the same object farther away from the sensor. Additional adjustments may be required to account for differences in size and background of the object and throughout the life of the sensor to compensate for the effects of the operating environment.
In conventional sensor systems, these gains are often adjusted by manual adjustment of a potentiometer. Unfortunately, in harsh industrial environments, these potentiometers can become dirty or noisy. Moreover, the potentiometers are frequently damaged by over or under adjustment and are prone to drift with time, component aging, vibration, etc. Furthermore, the fact that access to the sensors is required for routine adjustment can lead to a compromise in sensor location from the perspective of performance or safety. In some applications, significant system down time can be required to safely perform routine sensor adjustment and maintenance. Computer controlled sensors can be utilized to ameliorate some of these issues. However, the cost and size of computer controlled sensors has lead to poor acceptance in the marketplace.
The current state of the art in intelligent sensor architecture can be summarized in two approaches: 1) microcontroller based sensor units made to interface to discrete elements directly, creating high component count, fault susceptible, noise sensitive units; and 2) microcontroller based units made to interface to industry standard stand-alone ASICs, providing, inflexible component intensive solution with minimum ‘system visibility’.
Currently, the sensor market is dominated by large and expensive to manufacture sensor devices which are application specific (i.e. no onboard microcontroller control). Over the last few years there has been a slow introduction of microcontroller controlled sensors which offer few additional features over the older type sensors but at significant price/size premiums. With the exception of the microcontroller these sensors are architecturally equivalent to their predecessors. Both types of the sensor families provide support for a variety of features, but they do so by providing a host of sensor models individually tailored to the application with a minimum number of user programmable configuration options and with a price structure based on the overall volume associated with each model. Since the cost of these units is also volume dependent market penetration of non essential features tends to be limited. Furthermore, custom feature sets that might be desirable by some users require significant engineering to produce limiting the economic attractiveness of small volume users.